ummmm sorry to contradict but the 20v is a much better engine to start with as a base for a na buildup lol. Hence the reason Toyota used it for the formula Atlantic (only makes 240hp) is a 20v buildup. You can buy a formula atlantic from various sources but be prepared to spend the likes of 10-20k (depending on the supplier).
However you can get 200 out of a 16v, but anything past 170hp is going to get very pricy for only a few hp gains. unlike the easier stuff you do to get to 150-160.
Heres a good site to explain what I am trying to say.
Bill Sherwood's Modified 4AGE Page